This invention relates to a controller of a fixing unit of an electrophotographic color recorder, and particularly to a fixing process controller for an electrophotographic recorder suitable for fixing thick layers of a toner image.
The electrophotographic process involves charging, light exposure, development, image transfer and fixing. In color recording, toner images of colors are transferred to a sheet of paper, and thereafter, the toner is fixed. In portions of a picture, where many colors are used, the toner layers have an increased thickness, which necessitates fixing control. Among the conventional techniques, one disclosed in Japanese Laid-Open Patent Application No. 61-20970 (1986) enters information as to whether the recording picture is in a single color or multiple colors on the basis of an operator's judgement. Another technique disclosed in Japanese Laid-Open Patent Application 57-108876 measures the toner thickness in terms of toner consumption in the developer.
In color recording, the toner thickness extends as much as 3-4 times that of single-color recording, and the thickness of the toner layers must be taken into consideration for the fixing process. Faulty fixing results not only in the exfoliaton of toner, but also the degradation of color development due to insufficient fusion of lower toner layers, in color recording. Conversely, an excessive fixing process causes waste of power and premature breakdown of the fixing apparatus, and also offset and crease of paper in the case of heat fixing. On this account, it is difficult for the method of simple selection as described in the above-mentioned patent publication No. 61-20970 and the method described in the above-mentioned patent publication No. 57-108876 to have precise control over the toner thickness.